The sun’s strongest flare in 11 years might help explain a solar paradox

Physicists will test why the biggest flashes tend to occur as a solar cycle ebbs

SPOT OF BOTHER The same complicated sunspot spat out seven flares from September 4 to 10. This image shows in ultraviolet light the second-largest flare (bright flash at right), which was emitted on September 10.

SDO/GSFC/NASA

A series of rapid-fire solar flares is providing the first chance to test a new theory of why the sun releases its biggest outbursts when its activity is ramping down. Migrating bands of magnetism that meet at the sun’s equator may cause the biggest flares, even as the sun is going to sleep.

A single complex sunspot called Active Region 2673 emitted seven bright flares — powerful bursts of radiation triggered by magnetic activity — from September 4 to September 10. Four were X-class solar flares, the most intense kind. The strongest, released at 8:02 a.m. EDT on September 6, was an X9.3. The most powerful flare since 2006 (and the eighth largest since monitoring started in June 1996), it disrupted shortwave radio communication over Africa for up to an hour. It also flung a blob of energetic plasma, called a coronal mass ejection, speeding toward Earth, which sparked auroras the night of September 7 that were visible

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